Vinylidene fluoride resins are thermoplastic resins having favorable mechanical properties and exhibiting superior weather resistance, chemical resistance, and abrasion resistance. The resins are fabricated into various articles. Vinylidene fluoride resins are formed at a molding temperature of 200-350° C. by a molding operation such as compression molding, injection molding, extrusion molding, or blow molding. Because vinylidene fluoride resins are thermally deteriorated at such high molding temperatures, antioxidants are added in the same manner as in other plastics to ensure thermal stability during molding operations. For example, Japanese Patent Publication No. 44953/1978 discloses a composition comprising vinylidene fluoride resin and a stabilizer which is a combination of an organic phosphorous acid ester of polyhydric alcohol and pentaerythritol, dipentaerythritol, tripentaerythritol, or a mixture thereof. According to the invention of the publication, in the case using the resin as a paint composition almost no improvement in the deterioration time and adhesion time can be achieved by the composition prepared by the single addition of an organic phosphorous acid ester of polyhydric alcohol to a vinylidene fluoride resin. The deterioration time and adhesion time can be improved only in the case where 0.5-5 wt % of an organic phosphorous acid ester of polyhydric alcohol is added in the presence of 0.1-2 wt % of a polyhydric alcohol such as pentaerythritol, dipentaerythritol, or tripentaerythritol. In the observation of coloration of sheets which were press-molded on a heat press at 230° C., the effect of the addition of a phosphorous acid ester of polyhydric alcohol was confirmed when the organic phosphorous acid ester of polyhydric alcohol was added in the amount 0.5 wt % or more of the vinylidene fluoride resin, but not less than the amount of pentaerythritol which is also added simultaneously. This prior art document describes that even in this case, the products are colored, if 2 wt % of an organic phosphorous acid ester of polyhydric alcohol is added alone.
A phenol-type antioxidant is commonly used in the molding process of thermoplastic resins to improve the heat-resistant life. In the molding process of polypropylene at a temperature of 200° C. or higher where the resin is affected by a strong shearing force, a combined use of a phenol-type antioxidant and a phosphorus-type antioxidant is known to exhibit a synergistic effect. An antioxidant composition comprising a large amount of a phosphorus-type antioxidant, e.g. a composition containing a phosphorus-type antioxidant and a phenol-type antioxidant at a ratio of 3:1 to 1:1, is reported to be effective (Chemical Industry, April, pages 17-19, 1993).
Japanese Patent Application Laid-open No. 254769/1989 also discloses a method for improving heat stability of thermoplastic resins by the addition of a composition comprising a specific cyclic phosphite compound and a phenol compound to the thermoplastic resins. A specific proportion of the two compounds to be added disclosed by the patent application is an equivalent or smaller amount of a phenol compound for a given amount of a cyclic phosphite compound.
Vinylidene fluoride resins are known to be liable to cause various types of troubles when melt spun, due to their high melt viscosity and high viscosity during melt extrusion. Because of this, a plasticizer mutually soluble with vinylidene fluoride resins is added to decrease their melt viscosity and to provide the resins with softness. As one type of such plasticizers, aliphatic polyesters of an aliphatic dialcohol having 2-4 carbon atoms and an aliphatic dicarboxylic acid having 2-6 carbon atoms are known to exhibit excellent plasticizing effect while exhibiting minimal bleeding (Japanese Patent Application Laid-open No. 101114/1994). However, even such polyester plasticizers are not necessarily free from problems of bleed-out during and after a molding process.
Various types of compositions useful in the molding operation of thermoplastic resins are known in the art. However, there have been no vinylidene fluoride resin compositions which can sufficiently prevent a foaming phenomenon, coloration, and bleed-out of additives during molding operation.
As mentioned above, vinylidene fluoride resins have a high melt viscosity, require a high molding temperature, tend to deteriorate or decompose, or may get colored or produce foam. For this reason, various plasticizers have been added to vinylidene fluoride resins to avoid their deterioration or decomposition, and to improve their processability.
However, even in the composition of a vinylidene fluoride resin to which a plasticizer is incorporated, the vinylidene fluoride resin itself may be deteriorated or decomposed, the plasticizer may be thermally decomposed or produce foams during mold processing, and a bleeding phenomenon may occur during or after mold processing depending on its type and the amount added.
As mentioned above, the addition of a phosphite compound in combination with pentaerythritol to a vinylidene fluoride resin which does not contain a polyester plasticizer has been known in the art. According to the above prior art document, a vinylidene fluoride resin colored when 2 wt % of a phosphite compound was added together with pentaerythritol.
U.S. Pat. No. 4,957,953 discloses a composition comprising (1) a resin and (2) a stabilizer system of at least one monopiperidine compound and at least one polypiperidine compound for improving weathering properties of the resin, in particular light resistance. The resin may be polyvinylidene fluoride. The stabilized resin composition may contain a phenol antioxidant and a phosphorous-containing compound. This patent does not disclose a polyester plasticizer. Accordingly, the patent does not recognize or appreciate that a phenol compound and a phosphite compound can prevent foaming, coloration, and bleed-out of plasticizer during a molding operation. In addition, the patent does not disclose the production of fibers or fishing lines.
U.S. Pat. No. 6,054,538 discloses a composition comprising vinylidene fluoride copolymers, polyvinyl chloride, and methacrylic polymer. The compositions exhibit improved dielectric properties and are used for sheathing cables. According to this patent, vinylidene fluoride polymers have inferior dielectric properties. The composition may also contain a lead-containing thermal stabilizer and a plasticizer. This patent does not disclose any phenol or phosphite compounds. The patent also does not recognize or appreciate that a phenol compound and a phosphite compound can prevent foaming, coloration, and bleed-out of plasticizer during a molding operation. Further, the patent does not disclose the production of fibers or fishing lines.
As a result of extensive studies, the present inventors have found unexpectedly that when a small amount of a phosphite compound is added independently to a composition comprising 100 parts by weight of vinylidene fluoride resin and 2-20 parts by weight of polyester plasticizer (specifically, when 0.01-0.5 parts by weight of a phosphite compound is added to a composition comprising 100 parts by weight of vinylidene fluoride resin), such a vinylidene fluoride resin composition can exhibit superior heat resistance and controlled thermal deterioration at a temperature of 280° C. or higher, and can be formed without being colored or without producing foams. The inventors have further found that if a specific amount of phenol compound is added to this composition, not only the foaming phenomenon and coloration at higher temperatures can be prevented, but also tackiness due to bleed-out of plasticizers can be prevented through the product life. These findings have led to the completion of the present invention.
An object of the present invention is therefore to provide a vinylidene fluoride resin composition which is stable and free from a foaming phenomenon, coloration, and bleed-out of additives during molding operation. Another object of the present invention is to provide a molded product made from such a vinylidene fluoride resin composition.